The present invention relates to a copying system comprising a copying machine main body and its peripheral equipment (optional devices) such as an ADF (automatic document feeder), a sorter, a special copying paper cassette and the like connected thereto, and more specifically to an interface system for transmitting data (signal) between the main body and the respective devices.
Interface systems between the copying machine main body and the respective devices include one signal for one line system, a parallel communication system, and a serial communication system.
Although the one signal for one line system permits a realtime response, it requires I/O ports and cables as many as the necessary number of signals As the optional devices have improved functions, the number of I/O ports are increased for transmitting a lot of data and a large load and many cables must be processed on the side of a main circuit with increasing cost Further, in order to permit many kinds of optional devices to be mounted on a single main body it is necessary that the main body device be provided with the required number of signal lines for optional devices in advance. However, when the optional devices are not mounted, terminals are not used, which reduces efficiency.
The parallel communication system can transmit, for example, 8 bits of data at a time for high speed data communication. However, since it requires at least eight transmission cables (lines) and I/O ports, a large load is imposed on the side of a main circuit and all of the respective lines must be protected against noise.
Although the serial communication system has a slow transmission speed because it transmits data through a single signal cable successively, it can transmit a lot of data using two communication cables and two I/O ports so that the device has advantages that a lesser load is imposed when cables and a main circuit are processed, expansion of an interface is improved, cost is reduced, and only two cables are necessary to be protected for the prevention of noise. However, to increase a transmission speed, a frequency of signals is necessary to be increased, which reduces resistance to noise so that an improved measure for cable noise is required In addition, malfunction due to a communication error or the like must be prevented by software of a CPU of a main body serving as a host.
Then, as shown, for example, in Japanese Unexamined Patent Publication No. 254060/1985, there is proposed a device wherein a sorter is connected to a copying machine main body on-line, the sorter applies a signal indicating its capacity to the main body, and a condition for creating an image is restricted on the side of the main body depending on the signal for preventing improper sorting. With a conventional device such as the example, since addresses and commands inherent in respective optional devices are not admitted. signal lines are necessary for each kind of an operation mode.
Further, as shown, for example, in Japanese Unexamined Patent Publication No. 63565/1985, the use of an adapter having a serial interface circuit and a parallel interface circuit is proposed for permitting devices of which interface (communication) system has different specifications to be connected. A system employing such an adapter, however, has difficulty in coping with an increase in the kinds of optional devices and an increase in their functions.
In addition, since a signal in the conventional interface systems is a dedicated signal for each optional device, a different kind of an optional device cannot be connected to a main body or it is necessary that a mode be modified by a dip switch or through simulation to employ the different kind of the device.